They have nicknames like cartoon characters. But Marcola, Starfruit and Macarroni  the men Brazilian authorities believe ordered the most shocking weekend of violence in Sao Paulo's history  are no laughing matter. They're the mafiosi who run the First Command of the Capital (PCC), Sao Paulo's predominant organized crime faction. And now they've proved they are shrewd, ruthless and powerful enough to bring a place like Sao Paulo, Brazil's most important state and South America's largest city, to its knees with just a phone call from their jail cells. Just as important, the five-day-long attacks that left 137 people dead are evidence that what these gang bosses do over the next few months will not only affect the day-to-day lives of 40 million Paulistas  they could also help decide the upcoming election for Brazil's president.

Brazil  especially its second-largest city, Rio de Janeiro  has seen gang rampages before. But the mayhem in Sao Paulo set an astonishing new benchmark. It erupted last week after authorities transferred 756 gang-affiliated prisoners in an attempt to thwart what they believed would be a state-wide prison rebellion on the eve of Mother's Day, when family visits often provoke unrest. The PCC's reaction was swift. On Thursday night, bandits armed with grenades and machine guns attacked police stations and left five officers dead. Over the weekend they stepped up their attacks with a series of bombings, ambushes and drive-by shootings that took the death toll to 52. And on Sunday, they bombed 11 banks and a shopping center and burned more than 80 buses.

The carefully choreographed violence paralyzed Sao Paulo state and especially the state capital of the same name, a city of 19 million people that is Brazil's financial and industrial center. With hysterical rumors of more attacks spreading via the Internet on Monday, schools, offices and businesses sent people home early and the megalopolis was brought to a standstill by traffic jams on Monday afternoon as frightened citizens rushed home. By evening, the city streets were eerily empty as people cowered in their houses. "This was a landmark event for Sao Paulo in particular and for Brazil as a whole," said Sergio Mazina, vice president of the Brazilian Institute for Criminal Sciences. "Nothing like this has ever happened before."

Since taking office in 2003, President Luiz Inacio Lula da Silva has pledged to tackle both Brazil's security malaise and the inexcusable social conditions that have bred the gang violence. His opponent in the upcoming October election, former Sao Paulo governor Geraldo Alckmin, has boasted the state had triumphed over organized crime. The Sao Paulo crisis is likely to shine the spotlight on both their records."You can't say the PCC want to benefit one candidate or another, but there 's no doubt that they are smart and well-informed and that they know authorities are more vulnerable in an election year," said Bruno Paes Manso, an expert on the PCC and author of the book The X Man: A Look into the Soul of the Sao Paulo Assassin. "President Lula will be criticized for not investing more in public security, but Alckmin will be the one that is hurt most because this hasn't happened in the rest of the country."

The relentless bloodshed has sparked a vociferous debate over what do about Brazil's violent criminals and its notoriously corrupt and overcrowded prison system. Hardliners are arguing for a crackdown, while liberals counter that nothing will change unless the government attacks the country's epic social and economic inequality. But the question is not just what to do but how. Roughly a third of all Brazil's prisoners are locked up in Sao Paulo state; between 800 and 1,000 more prisoners are jailed each month and the system is stretched to the breaking point. "We'd need to build a new prison each 15 days to hold these new inmates," Mazina said. "And then we'd need to hire and train people to run them. This is a country that doesn't have the fiscal or structural conditions to provide health, education or housing, so how can we invest massively in prisons?"

Whatever action is taken, it is unlikely that the PCC will quietly fade away. The group runs most of Sao Paulo's 109 jails and will continue to challenge the state unless they are allowed to retain some control over an empire that includes drug trafficking, armed robbery and kidnapping, said Renato Simoes, a human rights expert who has followed the rise of the group. "I think it's a power struggle," said Simoes, a Sao Paulo state congressman who serves on the state's Human Rights Commission. Whatever happens, Paulistas are afraid, and with good reason. Marcola, Macaroni and Starfruit are the ones calling the shots, and few people trust authorities to keep them safe.